Conventionally, there has been a roughing end mill on which a plurality of cutting inserts is removably mounted, as one type of indexable rotary cutting tool for the purpose of providing highly-efficient work. This tool has a cylindrical tool body that is provided with a plurality of grooves extending from its base end side toward its leading end side in a peripheral surface of the tool body and a plurality of cutting inserts is removably mounted along the grooves. Since the plurality of inserts arranged in a direction of a rotational axis of the tool body is involved in cutting in such roughing end mill, the depth of cut provided by the tool is significantly large. Accordingly, by feeding the tool in a horizontal direction relative to a workpiece while maintaining such a large depth of cut, a highly-efficient cutting process can be performed.
As one example of such roughing end mills, Patent Document 1 discloses a type of roughing end mill which uses cutting inserts having a triangular shape in a planar view. The cutting inserts used in Patent Document 1 are of a positive type and each cutting insert has three corners that can be used for cutting. In addition, the cutting inserts are not arranged so as to be overlapped with each other in a direction along a tool rotational axis in one groove, and the cutting inserts are arranged at regular intervals.